A report released Wednesday from Enders Analysis appears to back
up that claim — at least when it comes to a sample of news
websites.

Enders conducted a small-scale experiment in which its
researchers requested eight web pages from a number of "popular
publishers" using a browser that impersonated an iPhone 6. The
researchers compared data usage when a full page loaded without
an ad blocker, with an ad blocker, and with an ad blocker and
JavaScript disabled:

The distribution of mobile data transferred on news
websites. A video was responsible for the big JavaScript outlier
on the left.Enders
Analysis

The study found that ad content accounted for between 18% and 79%
of the mobile data transferred, depending on the site. JavaScript
elements — often used by publishers for ads, but also for visual
elements such as animations — added an extra 6% to 68%. Enders
noted that the JavaScript it came across in the study wasn't
central to the articles being loaded.

The researchers concluded that it is reasonable to say
advertising accounts for half of all the data used by publisher
pages loaded over mobile data networks on the iPhone 6.

"Publisher mobile pages are bloated and advertising is an
enormous part of that," Enders says in the study.

Entry-level mobile data plans start at around 500MB/month —
which Enders says could be used to load the text of the King
James Bible around 100 times. So "resource-hungry" advertising
could clearly become a concern for some users. That's not to
mention that ads can increase page-load time, Enders adds.

Google, Apple, and Facebook have all recently rolled out options
for publishers to help reduce the "bloat" of ads within
their articles and increase page load times — while
still generating revenue — with the launches of
Google AMP,
Apple News, and
Facebook Instant Articles. However, while all three of the
initiatives have scores of publishers on board, many publishing
executives are wary about handing too much control of their
distribution over to third-parties.